The invention relates to a pressure regulator and, more particularly, to a pressure regulator having a double-seated valve arranged between a supply pressure and control pressure chamber including a fixed, outer valve seat arranged between the supply pressure chamber and the control pressure chamber which can be connected to a load. A moveable inner valve seat coaxial to the outer valve seat is arranged between the control pressure chamber and a pressure-relief chamber. A valve closing element cooperates with the valve seats and is loaded in a closing direction by the supply pressure in the supply pressure chamber and by a valve closing spring. The valve closing element rests on the outer valve seat in the closed position. The valve closing element has an axially displaceable control piston bearing the inner valve seat on its end side and has an axial pressure-relief chamber. The external diameter of the control piston is greater than the external diameter of the inner valve seat. The control piston is loaded in the opening direction by the control pressure in the control pressure chamber and in the closing direction by a control spring which counteracts the valve closing spring. In the closed position, the control piston rests with the inner valve seat against the valve closing element, and has a manually operable actuating element for changing the initial stress of the control spring.
Such pressure regulators, as disclosed, for example, in German Patent Documents DE 31 44 247 A1 or DE 29 08 097 A1, are used, inter alia, for the pneumatic adjustment of upholstered seat contours of orthopedic vehicle seats. Depending on the level of pressure of the control pressure which can be tapped off at the output of the pressure regulator, the upholstered seat contour assumes different shapes and can thus be individually matched to the desires of the passenger. The pressure level is set manually by means of an actuating element usually constructed as a manual selection wheel which, when performing adjustment, changes the initial stress of the control spring. If the actuating element is adjusted in the direction of greater control pressure, the valve closing element is lifted off the outer valve seat by the control piston as a result of the now stronger spring initial stress, so that a connection is made between the supply pressure chamber and the control pressure chamber. The control pressure prevailing in the control pressure space increases until the sum of the supply pressure and valve closing spring forces on the valve closing element is greater than the difference of the control spring and control pressure forces on the control piston. When the actuating element is rotated in the other direction for the purpose of setting a lower control pressure, the control piston lifts off from the valve closing element with its valve seat as a result of the reduced initial stress of the control spring and thus makes a connection between the control pressure chamber and the pressure-relief chamber connecting to the surrounding atmosphere. The control pressure in the control pressure chamber drops until the force exerted by it on the control piston is smaller than the spring force of the control spring. At this moment, the control piston is placed against the valve closing element again and the valve seat closes.
As a result of component friction and necessary pressure forces of the control spring and valve closing spring for the purpose of sealing the valve seats, the pressure regulator exhibits a hysteresis. That is, an adjustment movement of the actuating element in the direction of control pressure increase, up to a specific actuating element position, leads to a substantially different pressure level of the control pressure from that of an adjustment movement of the actuating element in the direction of control pressure reduction as far as the same actuating element position. Such a hysteresis behavior of the pressure regulator is a substantial disadvantage if--as is usually the case with orthopedic vehicle seats--there are memory aids on the actuating element which are intended to make it possible for each user to remember his individually desired upholstered seat contour. The individual seat contours are finally set after lengthy trials, by virtue of the mark, e.g. number, appearing at the actuating element position and permits the individually matched upholstered seat contours to be found again quickly. It can be found quickly even after it has been changed, without the renewed, wearisome and lengthy trials. In view of the hysteresis behavior of the pressure regulator, these memory aids however are of little use since the user sets different control pressures upon finding the mark again depending on whether he transfers the actuating element into the desired setting from a setting for higher control pressures or from a setting for lower control pressures. 5 The pressure control valve described in U.S. Pat. No. 35 59 688 is also a double-seated valve. In this valve, the valve element is loaded by a double control piston and a valve closing spring, and controls, together with the outer valve seat, the connection from a first valve port to a second valve port and, together with the inner valve seat, the connection between the first valve port and a ventilation outlet. The initiation of the pressure increase and pressure reduction process does not occur by means of a manual actuating element but rather by changing the pneumatic control pressure in a control chamber delimited by the double control piston. This pressure control valve also exhibits the described control hysteresis.
The invention improves a pressure regulator of the above described type in such a way that, irrespective of the adjustment direction of the actuating element, a control pressure of unvarying magnitude is always associated with a specific setting of the actuating element, so that the specific expected control pressure at the output of the pressure regulator in a reproducible manner.
The present invention is achieved with a pressure regulator having a double-seated valve arranged between a supply pressure and control pressure chamber including a fixed, outer valve seat arranged between the supply pressure chamber and the control pressure chamber which can be connected to a load. A moveable inner valve seat is coaxial to the outer valve seat and arranged between the control pressure chamber and a pressure-relief chamber. A valve closing element cooperates with the valve seats and is loaded in a closing direction by the supply pressure in the supply pressure chamber and by a valve closing spring. The valve closing element rests on the outer valve seat in the closed position. The valve closing element has an axially displaceable control piston which bears the inner valve seat on its end side and has an axial pressure-relief chamber. The external diameter of the control piston is greater than the external diameter of the inner valve seat. The control piston is loaded in the opening direction by the control pressure in the control pressure chamber and in the closing direction by a control spring which counteracts the valve closing spring. In the closed position, the control piston rests with the inner valve seat against the valve closing element and has a manually operable actuating element for changing the initial stress of the control spring. The pressure regulator further comprises a lifting device which, on being activated, displaces the control piston in the opening direction by a predetermined amount of travel while lifting the inner valve seat off the valve closing element. An actuating element couples to the lifting device in such a way that, at the start of the adjustment movement of the actuating element out of any adjustment position in the direction of the reduction of the control pressure, the lifting device is briefly activated in such a manner that the control pressure drops below the desired pressure to be reached. As a result of which, after deactivation of the lifting device, the desired pressure is reached as a result of increasing the control pressure.
In the pressure regulator according to the present invention, the slightest adjustment of the actuating element in the direction of control pressure reduction unavoidably lifts off the control piston from the valve closing element in a superproportional or overproportional manner. This brief lifting off results in a brief, superproportional pressure reduction in the control pressure chamber. However, since the lifting unit is immediately deactivated again, that is to say it becomes inactive, the subsequent control process of the pressure regulator is not further disturbed. The excessively high pressure loss in the pressure control chamber is now compensated again in that the control piston lifts off the valve closing element from the outer valve seat and a fluid short circuit is established between the pressure supply chamber and control pressure chamber. As a result of which, the control pressure increases until the valve closing element closes the outer valve seat again. The desired setting of the adjustment element is thus always attained in the pressure regulator by increasing the control pressure - and never by reducing the control pressure so that the state of equilibrium of the double-seated valve is always set from the same direction, namely by pressure increase. Thus, the hysteresis occurring when setting the state of equilibrium if the latter is attained by pressure reduction in the control pressure chamber is eliminated. In the pressure regulator according to the present invention, each setting of the actuating element is thus assigned a fixed control pressure which reliably prevails at the output of the pressure regulator whenever the actuating element assumes the associated position. This occurs regardless of the direction from which the actuating element has arrived at this setting.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.